The delivery of a carbureted mixture in the combustion chamber may be achieved, as it is known in the art, through parts moving in a reciprocating motion such as valves. A system of this type is protected by the applicant in French patent application FR-2,655,653.
However, engine performances may be limited by valve injection systems, notably concerning the control of the start and the end of the injection, and the valve area for the carbureted air (oscillation problems).
Furthermore, these systems must be mounted in cylinder heads of relatively large size. One improvement consists in using rotary plugs for the control and the delivery of a carbureted mixture.
French patent application FR-2,662,214 thus proposes the use of rotary plugs for controlling the pneumatic injection of fuel in a two-stroke engine.
The plugs disclosed have an axis of rotation located in a plane perpendicular to the axis of the cylinder, they are pierced with a transverse channel communicating the inlet pipe and the combustion chamber, and connected to driving means allowing them to be rotated according to the rotating speed of the engine crankshaft.
Compared with valves, such plugs can thus work at higher speeds and allow a higher flexibility as for the injection adjustment.
However, seal problems remain, notably at the plug inlet.
Seal devices are sometimes provided to that effect, either upstream or downstream from each plug, or in both places.
Patent application FR-2,559,208 relates to a plug for controlling the escape and/or the admission of gas from and/or towards a combustion chamber and onto which one or several seal devices are applied. The improvement envisaged in this prior art consists of a lubrication and of a cooling of the surface of contact between the seal device(s) and the plug.
It is not certain that this system is perfectly reliable, notably as far as sealing is concerned, because of the sophistication thereof.
Patent application FR-2,679,960 mentions a plug for which sealing at the inlet is provided by the shape and the lay-out of a channel pierced in the plug.
More precisely, this plug includes at least one channel through which the fluid flows, having one inlet port and one outlet port, the inlet port belongs to the lateral surface of the plug and is located at a distance, which is not zero, from the axis of rotation of the plug, whereas the outlet port belongs to the cylindrical surface of the plug and is radially offset with respect to the inlet port.
The delivery channel disclosed by this prior art includes an intrinsic fuel trapping means consisting of a bend formed by the channel and likely to hold back the fuel under the effect of the centrifugal force generated by the rotation of the rotary plug.